A standard disk brake has a caliper housing that fits over the edge of a brake disk and that is formed with a brakeshoe well aligned radially with this disk. A pair of brakeshoes in this well axially flank the disk and each have a brake pad turned toward the respective face of the disk and a backing plate turned away from it. Means such as a hydraulic piston-and-cylinder assembly built into the housing can urge the brakeshoes together against the disk for braking action.
It is standard practice, as known for example from German Pat. No. 1,263,412 filed Feb. 7, 1964 by Hans Schanz, to support the brakeshoes for axial displacement in the housing on a pair of axially extending pins. These pins are driven out to replace the brakeshoes. In such an arrangement a spring is normally provided to back the brakeshoes axially oppositely away from the disk when the braking operation is over, thereby minimizing drag on the disk and wear of the brakeshoes.
Such a return spring is seen in German Pat. No. 1,182,087 filed Dec. 5, 1962 by Hans Schanz. It is generally flat and cruciform. Two of its arms engage under the brakeshoe-support pins and the other two bear down on the brakeshoes at the front edges of the pads. Thus this spring urges the shoes apart while holding them snugly so that they do not rattle. This arrangement requires the use of a separate and relatively delicate return spring.
Another arrangement is seen in German patent document No. 2,845,959 filed Oct. 21, 1978 by Karl Fritz. Here the spring is formed of a spring-steel wire having a central bight that is hooked behind one backing plate that is specially formed, two loops at the ends of the bight that engage around the guide rods, and two legs which fit into respective generally axially open holes in the other specially formed backing plate. Such an arrangement is disadvantageous because, once again, it requires one to use a separate spring, and at the same time the two brakeshoes must be specially made to cooperate with it.
A simpler arrangement is seen in German Pat. No. 2,258,050 filed Nov. 27, 1972 and referring to U.S. Pat. No. 3,256,959. Here a simple hairpin wire spring is hooked under one of the brakeshoe-support rods and has a pair of radially inwardly bent ends that engage through slots formed in the brake pads with the backing plates so as to push the two backing plates apart. This gives effective and simple return action. In addition the spring wire is insulated, normally by being enameled, so that an electrical connection can be made from an alarm device to it. Since the pusher ends of the spring legs lie flatly against the backing plates, when the brake pad wears down to an axial thickness equal to the wire diameter, the brake disk will engage the wire, quickly wearing off its insulating covering and grounding it. When such a grounding is detected, the alarm device will signal that the brake pads are worn out. This arrangement still requires that several parts be removed and remounted each time the pads are changed, increasing the difficulty of the operation and the likelihood that something critical will be lost.